Flowmaster U-Fit Exhaust Kit Install - DIY Exhaust Pipes

Finishing our '63 Nova wagon V-8 swap

In the past couple of issues, we have shown how to build some pretty exotic headers and exhaust systems. We thought we might be missing a segment of do-it-yourselfers who are not ready to build a custom set of headers, but can definitely tackle welding up some pipes. In this issue we put the finishing touches on a mild V-8 swap into a ’63 Nova wagon. We used as many bolt-ons as we could, but when we got to the exhaust we just couldn’t find a bolt-on kit. Luckily, there are a few builder-type set-ups available, like the U-Fit exhaust kit from Flowmaster.

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The U-Fit kits are available in 16-gauge aluminized or stainless steel in 2.25-, 2.5-, and 3-inch diameters. The U-Fit kits include the front adapter pipes, intermediate pipes, H-pipe assembly, over-the-axle pipes, and your choice of optional tailpipe exits. Each piece has a slip-fit connection to ease assembly. The kit doesn’t include some of the things you’ll need to build a complete system, like mufflers and hangers.

For this early Nova’s 290-horse small-block crate engine, Flowmaster recommended the 2.25-inch system. This is plenty for the mild Mouse, but just as important, it gives us a bit more clearance for the steering area, which is pretty tight on this generation Nova with headers.

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We wanted this car to have that "Flowmaster sound" so we grabbed a set of the company’s 40 Series two-chamber mufflers. The 40 Series muffler delivers an aggressive exterior and interior tone. It is constructed of 16-gauge aluminized steel and fully MIG-welded. There are quieter options in the Flowmaster arsenal, but we are still into that aggressive exhaust sound so we stuck with the 40s.

Since it would be really difficult to shoot the pictures and do the work, we hooked up with Josh Gledhill, owner of The Muffler Man in Placentia, California, to install the system. Enlisting the help of a professional was the smart thing in our case--not that this is a super difficult job to do, but our welding skills leave a lot to be desired. Not only can Josh lay an awesome bead, he also clued us in on a bunch of tips that we’ll pass along to you.

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Flowmaster U-Fit Exhaust Kit Install - DIY Exhaust Pipes

1 Here is the 2.25-inch U-Fit kit from Flowmaster. It's made from mandrel-bent, 16-gauge aluminized steel tubing and comes with all the necessary bends and angles you need to do the job at home. You will need to pick up a set of mufflers, a hanger kit, and possibly some tips to round out the system. Some of the sections of pipe have an end that has a larger diameter. This is so you can slip it over another piece of pipe for easy install.

2 When it comes to the mufflers, there are many options to choose from in the Flowmaster line. Josh says "You want to look at the muffler's overall dimensions and check that against the space you have available under the car." This shot shows the difference in size between the 50 series (bottom) and the 40 series. The 50s are quieter, but are too big to fit without dropping them closer to the ground. We wanted a more agressive sound anyway, so we used the 40 series and also kept our ground clearance.

3 Josh tells us the first step is to do a quick lay out on the floor so you will know what pipes go where. Each pipe has a certain place it wants to be, but you can also change them up depending on your particular needs. There are a few pipes that are used for a specific spot, like the 90-degree bends that are used at the head pipes (in front of the muffler) and the two that come together to create the over-the-axle section (behind the muffler).

4 Josh noted the head pipe area is going to be the most challenging because there is less room, so he likes to start there. The head pipe will need to come down between the motor and framerails, and then point back. Keep in mind, in most cases the system needs to run under the transmission crossmember so bring down the head pipes so it's a straight shot. For rear-steer cars, like the Nova and Camaros, cycle the steering to determine the best route to take with the head pipe. In our situation, it worked out best to take the head pipe over the top of the steering arm on the driver's side. There was enough room to just come straight down on the passenger's side.

5 With the tape measure in hand, Josh marked out the first cut on the head pipe section. He recommends adding a 1/2-inch to the measurement before making the first cut on any pipe. It's much easier to trim off a little more to get it perfect than add a section back on.

6 There are many tools you can use to cut the pipe, from a simple hacksaw up to high-end cold saws. Unless you feel like getting a workout during your install, we would suggest using a power tool. A cut-off saw is a great option because they are fairly cheap (Harbor Freight has a 3.5hp one for 99 bucks) and will cut the pipes nice and straight.

7 After every cut, you should dress up the end--a grinder will do a good job on the OD. This will also give you the proper V in the weld area when it comes time to weld the pipes together.

8 A simple file can be used to knock off any slag inside the pipe.

9 Because of all the different types of collectors out there, it's a good idea to purchase the correct flanges from your header/manifold supplier, Sanderson in this case. With the collectors in place, Josh continued constructing the necessary Z-shaped head pipe for the driver side.

10 Even though all the pipe sections are pretty long, sometimes you will only need a little bit of it. Once you are happy with one section and its fitment, you can go ahead and put a few easy-to-access tack welds. We say "easy-to-access" because if you need to remove that section you will need to get in there with a grinder to remove the tacks.

11 The passenger side was much easier to route, and only required some trimming and a slight bend. Since we are in a pro shop, Josh just used his bender, but if you are at home you'll need to cut the pipe, put an angle on it, and then weld it back together. Josh also recommended trying to make the ends of the head pipes symmetrical, which will make the rest of the job much simpler.

12 With the head pipes designed, it was time to put the mufflers in their spots, which is normally right in front of the rear axle. This is usually the area under the rear seat and the floorpan, which is raised up to give the mufflers more clearance. Also, you can see that the mufflers are pretty close together while the head pipes are much wider. We hooked the two sections of tubing made specifically to bring the system close together to the head pipes. You want the system to run right next to the driveshaft, that's where the most room is.

13 As you make cuts, there will be leftover straight sections, and in our case two of them were used to connect the mufflers. On a side note, our driveshaft was next door at the time getting shortened so Josh put in a piece of pipe for now to make sure he left enough clearance for it.

14 With everything in front of the axle tacked in place, Josh put a set of hangers on the mufflers to support the system. In a dual system, you will need two hangers per side or four hangers total, one at the muffler and one at the tailpipe. The headers/manifolds will hold up the front. Online suppliers like Summit Racing offer hangers or you can contact your local muffler shop to score some.

15 Here is why symmetry is such a good idea when dealing with exhaust. If everything is in the same place, then you can get one piece perfect and then just match your cuts. That's what we did here, on the outlet of the muffler section.

16 Sometimes the best way to figure out where you need to cut the pipe is to just hold up the next piece and take a look.

17 When it comes to the over-the-axle section, it is best to get a second guy (Brandon Silva in our case) to help angle the pipes around for the best fitment. It's best to do this with the suspension at ride height so if you have the car on jack stands, make sure they are under the axle. This is also where you want to determine tip placement. We are sending it right out the back so having the pipe run straight is best for us. If you want your tips to exit out the side, then design that accordingly by articulating the sections so they point to the rear quarters.

18 Once the system is fully designed and tacked in place, take out as much as you can to weld the joints on the bench.

19 For the sections that just won't come out easily, you will need to weld them in place. Josh showed us the best way is to start at the 12 o'clock position and come down to the 6 o'clock position on one side of the pipe, then start at 12 and go to 6 on the other side.

20 The U-Fit kit also comes with an H-pipe assembly that includes two side pieces and two center sections of pipe. Our system was so close together that our two side pieces could be welded together to form the H-pipe. After installing the actual driveshaft, Josh placed the side piece up to figure out where it would fit without interfering with the shaft. Then he cut the holes with a torch.

21 Here is a good shot of the completed H-pipe assembly right before being welded. Josh recommends putting it as far forward as possible so you can still get the driveshaft out easily. An H-pipe is used to equalize the pressure in both exhaust pipes allowing the engine to see equal backpressure and improve performance. It also aids in reducing some back pressure, which hurts top end horsepower.

22 We had Josh throw down a couple tack welds to show what a good one should look like. The one on top is too cold so most of the weld sits above the pipe and the bottom one is too hot. The middle is what it should look like if you have your settings just right.

23 That completes the system except for adding a set of tips and finishing the H-pipe. Our system is tucked up as close to the floor pan as possible to give us the most ground clearance and the 40 series mufflers give the car a nice deep and raspy sound. So if you have a welder, chop saw, and some time, you can also hook up your ride with a U-Fit kit from Flowmaster. Josh charges $250 to install a kit like this if you provide the parts, so that should help you determine if its worth your time or not.